Process for the preparation of novel stabilized phosphorus ylides

ABSTRACT

Compounds of the formula (1) 
     
         Ph.sub.3 ═CH--C(R)═Nu                              (1) 
    
     wherein R is hydrogen, a C 1  -C 5  -alkyl, C 1  -C 3  -fluoroalkyl or perfluoroalkyl radical, an unfluorinated or fluorinated C 6  -C 14  -aryl radical or a group OCH 3  ; and 
     Nu is S, Se, C(CN) 2 , 
     NH, PhN, PhNHN, ##STR1## or a radical of the formulae (a), (b), (c), (d) or (e) ##STR2## wherein Z is C(CH 3 ) 2 , S or N(CH 3 ) and n=1 or 2 (provided that the combinations R═Ar, SAlk or OAlk and Nu═NPh, and the combinations R═H, Alk or aryl and Nu═S are excluded) are disclosed, as well as methods for making them.

FIELD OF THE INVENTION

This application is a division of application Ser. No. 08/640,161, filedApr. 30, 1996 now abandoned.

The present invention relates to novel stabilized phosphorous ylides andprocesses for their preparation. More particularly, the presentinvention relates to a process for substituting the carbonyl oxygen of2-formyl- or 2-oxoalkylidenetriphenyl-phosphoranes (OATP) by otherstabilizing groups to form novel compounds having an increased tendencyto form complexes or compounds which absorb in the visible region of thespectrum.

BACKGROUND OF THE INVENTION

The contents of the references cited in the specification are herebyincorporated by reference.

Synthetically valuable 2-oxoalkylidenetriphenylphosphoranes (OATP) areusually prepared in two ways. Either by reaction of triphenylphosphinewith α-haloketones and subsequent treatment of the resulting phosphoniumsalt with alkali metal hydroxide (M. I. Shevchuk et al., Zhurnal obsheiKhimii, Vol. 40, N 1, pp. 48-57, 1970) ##STR3## (R=alkyl, aryl oralkoxy) or by acylation of methylenetriphenylphosphorane with acylchlorides (H. J. Bestmann et al., Chem. Ber. 95, 1513, 1962) or reactivecarboxyl derivatives (Y. Sheng et al., Synthesis, 1984, p. 924-926).

    Ph.sub.3 P═CH.sub.2 +RCOX→Ph.sub.3 P═CH--COR

(R=alkyl, perfluoroalkyl or aryl; X=halogen, OR)

Some phosphorus ylides containing other stabilizing groups have beenprepared by reaction of phenylethynyltriphenylphosphonium bromide (II)with anilines, enamines or acetoacetate (H. Hoffmann et al., TetrahedronLetters N17, 1964, pp. 983-987)

    Ph.sub.3 P--C.tbd.CC.sub.6 H.sub.5 Br+H.sub.2 Nu→Ph.sub.3 P--CH═CC.sub.6 H.sub.5 Nu                             II III

    Ph.sub.3 P═CH.sub.2 +R.sup.1 --N═CR.sup.2 Cl→Ph.sub.3 P═CH--CR.sup.2 ═NR.sup.1                          IV V

or by acylation of methylenetriphenylphosphorane with imidoyl chloride(H. Yoshida et al., Synthesis 1977, pp. 626-628).

    Ph.sub.3 P═CH.sub.2 +R.sup.1 --N═CR.sup.2 Cl→Ph.sub.3 P═CH--CR.sup.2 ═NR.sup.1                          IV V

R¹ (V)=Ar; R² (V)=Ar, SAlk, OAlk

Some 2-thioxoalkylidenetriphenylphosphoranes (VII) have been prepared byalkylation of triphenylphosphine with thio derivatives (VI) (EP-A-052931); ##STR4## M (VII)=S; R¹, R² ═H, Alk, Aryl

Except for the above mentioned processes, it has not been possiblehitherto by the prior art to obtain phosphorus betaines having astabilizing group other than the carbonyl oxygen in the β position.Phenylethynyltriphenylphosphonium bromide (II), imidoyl chlorides (IV)and the alkylated (thio)carbonyl compounds are usually accessible withgreat difficulty, so that the preparation of phosphorus betainescontaining the above mentioned groups should be limited to only a fewexamples.

On the other hand, substitution of the oxygen by other groups havingdifferent steric and electronic properties would be an expedient way tomodify organic compounds.

SUMMARY OF THE INVENTION

The object of the invention is thus to provide a simple and economicprocess which enables the carbonyl oxygen of 2-formyl- or2-oxoalkylidenetriphenylphosphoranes (OATP) to be replaced by otherstabilizing groups and, in this manner, the reaction behavior or, e.g.,the complexing tendency of the entire molecule to be varied.

The present invention achieves this object and relates to novelcompounds of the formula (1) and a process for their preparation

    Ph.sub.3 P═CH--CR═Nu                               (1)

wherein R is hydrogen, C₁ -C₅ -alkyl, a C₁ -C₅ -fluoroalkyl orperfluoroalkyl radical, an unfluorinated or fluorinated C₆ -C₁₄ -arylradical or OCH₃ ; and Nu is S, Se, C(CN)₂, NH, PhN, PhNH--N═, ##STR5##or a radical of the formulae (a), (b), (c), (d) or (e) ##STR6## whereinZ is C(CH₃)₂, S or N(CH₃) and n=1 or 2; provide that the combinationsR═Ar, SAlk, or OAlk and Nu═NPh, and the combination R═H, Alk, or aryland Nu═S are excluded.

Compounds of the formula (1) are obtainable by first reacting 2-formyl-or 2-oxoalkylidenetriphenylphosphoranes with chlorinating agents to givecompounds of the formula (2)

    Ph.sub.3 P.sup.+ --CH═C(R)--Cl X.sup.-                 ( 2)

wherein X is Cl, Br or POCl₂, followed by reaction of compounds of theformula (2) with nucleophiles (Nu).

DETAILED DESCRIPTION OF THE INVENTION

Surprisingly, it has now been found that, in the reaction of2-formyltriphenylphosphoranes or 2-oxoalkylidenetriphenylphosphoraneswith a chlorinating agent, stable 2-chloroalkenylphosphonium salts ofthe formula (2) are formed. According to the known prior art, it wouldbe expected here that these compounds react, with hydrogen exchange, togive the corresponding α-chloro ylides (D. B. Denny et al. J. Org. Chem.27, 998 1962) or react, with oxygen exchange, to give thedichloroalkyltriphenylphosphonium salts.

The stoichiometric ratio of 2-formyl- or2-oxoalkylidenetriphenylphosphoranes to the chlorinating agent used is,according to the invention, generally 1:1.5 to 1:2.

Chlorinating agents which are preferably used are POCl₃, PCl₃, COCl₂,(COCl)₂, SOCl₂ or other conventional chlorinating agents. Thetemperature in the chlorination reaction is in a range from 60° to 150°C., preferably in a range from 90° to 120° C., with a reaction time inthe range from 30 to 90 minutes, in particular from 40 to 60 minutes.

The reaction proceeds in an organic, preferably chlorinated, solvent,such as carbon tetrachloride, chloroform or methylene chloride, but itcan also be carried out without solvent. The yields of2-chloroalkenylphosphonium salts are 80 to 100%, in particular >90%.

The phosphonium salts obtained in this manner can be reacted withvarious nucleophiles, such as Na₂ S, Na₂ Se, H₂ C(CN)₂,1,3,3-trimethyl-2-methylene-1,3-indole (Fischer base), CH₃ COOCH₂COOCH₃, CH₃ COCH₂ COCH₃ or with PhNH₂, PhNHNH₂ and NH₃ and compounds ofthe formulae below: ##STR7## where Z is O, S, N(CH₃)₂, or C(CH₃)₂,CH═CH, to give novel stabilized Wittig ylides of the formula (1).

The yields of compounds of the formula (1) in this reaction are in therange from 50 to 90%, preferably in the range from 70 to 90%.

The reaction of compounds of the formula (2) with nucleophiles iscarried out in organic solvents, such as methanol, ethanol, methylenechloride or acetonitrile. For this purpose, the appropriate nucleophileis employed in a stoichiometric or superstoichiometric proportion basedon the triphenyl-β-chloroalkenylphosphonium salt used. In particular,the ratio of nucleophile to compounds of the formula (2) is in the rangefrom 1:1 to 1:2.

The reaction time is in the range from 30 to 80 minutes, at atemperature in the range from 20° to 80° C., in particular from 20° to40° C.

The novel compounds of the formula (1) have, in comparison with thecorresponding compounds containing a carbonyl oxygen, a range ofinteresting properties. By replacing the carbonyl oxygen by sulfur,selenium or heterocyclic fragments, it is possible, for example, toobtain compounds having an increased tendency to form complexes orcompounds which absorb in the visible region of the spectrum and whichcan therefore be used, e.g., as sensitizers for silver halides inphotography, as precursors in the preparation of β-substituted cyaninedyes and for the synthesis of conjugated systems and as synthons for thepreparation of various heterocycles.

EXAMPLE 1 Preparation of Triphenyl-(2-chloroalkenyl) Phosphonium Salts

In a three-neck flask equipped with thermometer, cooler and bubblecounter, 20 mmol of the corresponding triphenyl-β-oxophosphorane and 40mmol of POCl₃ are heated at 100° C. for 60 to 90 minutes. The excess ofPOCl₃ is distilled off in vacuo, the residue is washed three times withdiethyl ether and dried in vacuo.

a. Triphenyl-(2-chloroprop-1-enyl)phosphonium dichlorophosphate:

Yield: 92%

Melting point: 105°-107° C.

b. Triphenyl-(2-chloro-3,3-difluoroprop-1-enyl)phosphoniumdichlorophosphate:

Yield: 94%

Melting point: 150°-152° C.

C. Triphenyl-(2-chloro-3,3,3-trifluoroprop-1-enyl)phosphoniumdichlorooxyphosphate:

Yield: 91%

Melting point: 110°-112° C.

EXAMPLE 2 Preparation of Triphenylphosphoranylidenealkane-2-thiones

50 mmol of the corresponding triphenyl-β-chloroalkenylphosphonium saltare stirred together with 100 mmol of Na₂ S in 50 ml of methanol for onehour at 20° C. The reaction mixture is diluted with 100 ml of water andthe organic phase is extracted twice with dichloromethane. The extractis dried over sodium sulfate and filtered and the organic solvent isdistilled off in vacuo. The residue is recrystallized from a CH₂ Cl₂:hexane mixture.

a. 3-(Triphenylphosphoranylidene)propane-2-thione

Yield: 89%

Melting point: 180°-182° C.

b. 1,1-Difluoro-3-(triphenylphosphoranylidene)propane-2-thione

Yield: 71%

Melting point: 146°-148° C.

c. 1,1,1-Trifluoro-3-(triphenylphosphoranylidene)propane-2-thione

Yield: 74%

Melting point: 162°-164° C.

d. 1-Phenyl-2-(triphenylphosphoranylidene)ethanethione

Yield: 84%

Melting point: 164°-166° C.

EXAMPLE 3 Preparation of1,1-Difluoro-3-(triphonylphosphoranylidene)propane-2-selenone

50 mmol of triphenyl-(2-chloro-3,3-difluoroprop-1-enyl)phosphoniumoxochloride are stirred with 100 mmol of Na₂ Se in 50 ml of methanol forone hour at 20° C. The reaction mixture is diluted with 100 ml of water,the organic phase is extracted twice with dichloromethane and dried oversodium sulfate. The solvent is filtered off and then distilled off invacuo. The residue is recrystallized from a CH₂ Cl₂ :hexane mixture.

Yield: 52% Melting point: 149°-151° C.

EXAMPLE 4 Preparation ofTriphenylphosphoranylidenealkylethylidelidenemalononitriles

50 mmol of the corresponding triphenyl-β-chloroalkenylphosphonium saltare stirred together with 50 mmol of malonodinitrile in 40 ml of ethanoland 100 mmol of triethylamine for one hour at 20° C. The precipitate isfiltered off and the product recrystallized from ethanol.

a. 1-(Triphenylphosphoranylidene)methylethylidenemalononitrile

Yield: 88%

Melting point: 266°-268° C.

b.2,2-Difluoro-1-(triphenylphosphoranylidene)methylethylidenemalononitrile

Yield: 72%

Melting point: 211° C.

c.2,2,2-Trifluoro-1-(triphenylphosphoranylidene)methylethylidenemalononitrile

Yield: 90%

Melting point: 234°-236° C.

d. 1-(Triphenylphosphoranylidene)phenylethylidenemalononitrile

Yield: 61%

Melting point: 238°-240° C.

Although certain presently preferred embodiments of the invention havebeen described herein, it will be apparent to those skilled in the artto which the invention pertains that variations and modifications of thedescribed embodiments may be made without departing from the spirit andscope of the invention. Accordingly, it is intended that the inventionbe limited only to the extent required by the appended claims and theapplicable rules of law.

What is claimed is:
 1. A compound of the formula (1)

    Ph.sub.3 P═CH--C(R)═Nu                             (1)

wherein: R is hydrogen, a C₁ -C₅ -alkyl, C₁ -C₃ -fluoroalkyl orperfluoroalkyl group, an unfluorinated or fluorinated C₆ -C₋ -aryl groupor a OCH₃ group; and Nu is C(CN)₂ provided that the combinations R═Ar,or Oalk and Nu═NPh, and the combination R═H, Alk, or aryl are excluded.2. The compound of claim 1 which is1-(triphenylphosphoranylidine)methylethylidenemalononitrile.
 3. Thecompound of claim 1 which is2,2-difluoro-1-(triphenylphosphoranylidene)methylethylidene-malononitrile.4. The compound of claim 1 which is2,2,2-triffloro-1-(triphenylphosphoranylidene)methylethylidenemalononitrile.5. The compound of claim 1 which is1-(triphenylphosphoranylidene)phenylethylidenemalononitrile.